The present disclosure relates to charged particle beam microlithography systems used for the fabrication of integrated circuits. More specifically, the disclosure pertains to the systems and methods for passing high energy charged particles through mask reticles and the alignment of the particle beams to wafers within the microlithography systems.
The manufacture of integrated (IC) circuits requires the use of many microlithography process steps to define and create specific circuit patterns and components onto the semiconductor wafer. As IC device performance demands migrate to higher levels, lithography technology has evolved both to higher performance levels as well as to new and additional process applications. Microlithography has expanded from the traditional use of photo energy to transfer circuit/component images onto the wafer substrate, to the use of charged particle beams such as electron, proton and molecular beams for both circuit imaging and substrate modifications. For example, high performance ICs may require the fabrication of semi-insulator regions on a wafer for improved circuit/component isolation, high Q inductors for high signal frequency stability and high resistance structures for specific circuit components. Charged particle beam (CPB) microlithographic processes are commonly used to fabricate the above said regions and components.
FIG. 1 illustrates a conventional charged particle beam (CPB) microlithography system 100. Such system comprises of a CPB source 102 to generate a charged particle beam to travel through the microlithography system along the particle beam axis 104 within the system to eventually strike the wafer 106 located on a wafer stage 108. After exiting from the source 102, the CPB 110 may pass through, if needed, various beam apertures 112 and beam lens/deflection subsystems 114 before transmission through a mask reticle 116 that is mounted upon a mask stage 118. After passing through the mask reticle, the now imaged CPB may pass through additional beam lens subsystems 120 to focus and project the CPB onto the target wafer 106. It is noted that various CPB microlithography systems may incorporate various beamline designs such that apertures 112 and beam lens subsystems 114 and 120 may be of different quantities, designs and lengths.
FIG. 2a is a side view and FIG. 2b is a top view of a typical mask reticle used within conventional CPB microlithography systems. The mask reticle 200 features at least two alignment markers 202 used for the purpose of aligning the mask reticle 200 with a wafer so that the mask pattern image(s) on the mask reticle 200 is aligned to a predetermined targeted substrate area on the wafer. The mask pattern image(s) is usually located within a mask target area 204 by which the CPB is transmitted through. The mask target area 204 is usually the center area of the mask reticle 200, and the alignment markers 202 are located in outside perimeter areas.
For conventional CPB systems employing high energy particle beams such as proton beams greater than certain level of energy (i.e., 3 MeV (million electron-volts)), there are serious issues associated with the use of such proton beams. High energy particles are particles projected at higher velocities and of higher power, generating additional heat loads for the CPB system. Heat from the CPB induced upon the system may cause damage to the system components enough to disturb the alignment integrity of the imaged beam to the targeted wafer. Heat damage to the imaging mask reticle may result with distorted, improper images on the wafer.
Referring back to FIG. 1, the higher energy particles may have more divergence upon exit from the aperture 112 as well as the mask reticle, enough to create distorted, improper images onto the wafer. Furthermore, there is no good controlling mechanism like the deflection subsystem 114 to control the flow of the particles. Also, the distance 122 between the mask reticle 116 and the wafer 106 in a conventional system tends to be too big to handle high energy particles due to the divergence.
In addition, high energy CPBs may produce higher levels of incidental harmful nuclear radiation emitting throughout the system, especially on the mask reticle itself. As the mask reticles are placed and transferred to different locations in the manufacturing facilities, they may cause great concerns when they become radiation sources. Further, the current mask reticle or other masking materials associated therewith are not well suited for precisely controlling and transmitting the proper collective beam energy upon each predetermined area of the wafer.
What is needed is an improved method and system for sufficiently and efficiently resolving the above issues related to the use of high energy CPBs.